A Red Cross worker delivers bedding materials to an apartment unit at The Ivy Apartments, where a man diagnosed with the Ebola virus was staying in Dallas, Texas October 2, 2014. REUTERS/Mike Stone

A cleanup crew began its decontamination work at the Dallas apartment complex where the first person diagnosed with Ebola in the United States had been staying before he was admitted to the hospital five days ago and where he remained in serious condition on Friday.

Four people close to the Ebola patient, Liberian national Thomas Eric Duncan, "will remain in the apartment during this time and it is safe for them to do so," Dallas County said in a statement.

Sheets and other items used by the man have been sealed in plastic bags, but questions have been raised about the delay in sanitizing the apartment since Duncan's diagnosis was confirmed.

Senior Obama administration officials were scheduled to hold a news conference on Ebola at 3.30 p.m. EDT as the Pentagon said it could increase the number of military personnel being sent to West Africa to help with the outbreak there.

A crew from the Cleaning Guys, a hazardous materials cleanup company, arrived about 11:30 a.m. CDT (12.30 p.m. EDT) to start the work that officials said would take about three hours. Along with the cleanup crew, three fire and rescue vehicles also arrived at the apartment complex in a northeastern part of Dallas, including an ambulance and a fire truck.

A county official said the cleaners will place materials in containers and take them to a secure location. Duncan is being treated at Texas Health Presbyterian Hospital. Officials said a disposal vendor was in place to remove any potentially contaminated materials from the hospital.

U.S. health officials say they are confident that they can prevent the spread of the Ebola virus in the United States.

The case has put authorities and the public on alert over concerns that Ebola could spread from three impoverished West African countries, Liberia, Guinea and Sierra Leone, where the virus has killed at least 3,338 people.

On Friday, Howard University Hospital in Washington said it admitted and isolated a patient with possible symptoms of Ebola who had recently traveled from Nigeria "in an abundance of caution." The CDC says outbreaks in Nigeria and Senegal appear to have been contained.

As part of the U.S. effort to help contain the spread of the deadly virus, the Pentagon on Friday said the number of military personnel that could be deployed to West Africa could reach nearly 4,000, more than earlier estimates of about 3,000.

"We project that there could be nearly 4,000 troops deployed in support of this mission but we are obviously assessing the requirements on a daily basis," said Rear Admiral John Kirby, the Pentagon press secretary. "It may not go that high."

Up to 100 people had direct or indirect contact with Duncan, and Texas health officials said about 50 are now being monitored daily. Of those, 10 were described as being "at high risk." Ebola, which can cause fever, vomiting and diarrhea, spreads through contact with bodily fluids such as blood or saliva.

EBOLA WASTE DISPOSAL

The critical issue of how hospitals in the United States should handle and dispose of medical waste from Ebola patients is being addressed, the government said. The U.S. Department of Transportation said it expects to release new guidelines later on Friday that will allow hospitals in Texas to safely dispose of Ebola-infected medical wastes.

Most U.S. hospitals are not equipped with incinerators or large sterilizers called autoclaves that could accommodate the large amounts of soiled linens, contaminated syringes and virus-spattered protective gear generated from the care of an Ebola patient, said Dr. Jeffrey Duchin, chair of the Infectious Diseases Society of America's Public Health Committee.

In Dallas, four people close to Ebola patient Duncan were quarantined in the apartment where he stayed as health officials widened their search for others who had direct or indirect contact with him.

NBC News said on Thursday that one of its freelance cameramen, Ashoka Mukpo, 33, had contracted Ebola in Liberia, the fifth American to be diagnosed. NBC said he had quarantined himself after feeling ill and discovering he had a fever.

NBC has said the entire crew would return to the United States on a private plane and remain under quarantine for 21 days, the maximum incubation period for Ebola.